Counterflow helical heat exchanger

ABSTRACT

A heat exchanger assembly comprising a tube with a thermally conductive tube insert sealed therein, the tube insert having a substantially similar cross-section to the cross-section of the tube, and a plurality of fluid ports for passage of fluid into and out of the tube, the fluid ports arranged for counterflow operation. The tube insert includes a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle. The tube insert is sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices.

RELATED APPLICATIONS

This application claims priority to U.S. Application No. 61/980,274, filed on Apr. 16, 2014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to heat exchangers and, more particularly, to liquid-to-liquid heat exchangers for use in comparatively smaller spaces, such as in automobiles or other motor vehicles.

2. Description of Related Art

Designers of heat exchangers for use in automobiles and other motor vehicles are constantly striving to obtain increased heat transfer capability in a smaller space. In the field of liquid-to-liquid heat exchangers, the use of turbulators on the hot fluid side and extended surface, such as a sintered metal matrix, on the cool fluid side, are well-known approaches to the problem. Increasing the flow path length of the fluids while maintaining reasonable fluid pressure drops is another approach to increased heat transfer, but it is not usually possible to accomplish this in a smaller space.

Therefore, a need exists for an improved heat exchanger with superior heat transfer capabilities, which would provide for optimum performance at the least possible cost while utilizing standard liquid-to-liquid heat exchanger manufacturing techniques, and providing the same in an equivalent- or smaller-sized package.

SUMMARY OF THE INVENTION

Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved heat exchanger assembly which can provide equivalent or superior heat transfer performance in a smaller package.

It is another object of the present invention to provide an improved heat exchanger which provides a considerable increase in flow path length, and consequently an increase in heat transfer, for a given tube length.

A further object of the invention is to provide an improved heat exchanger which allows for counterflow operation, providing optimum heat transfer performance.

It is yet another object of the present invention to provide an improved heat exchanger which makes use of standard aluminum liquid-to-liquid heat exchanger manufacturing techniques, such as inner tube expansion and cab (controlled atmosphere brazing) furnace flux brazing.

It is still another object of the present invention to provide an improved heat exchanger which includes a helical tube insert, thereby creating two fluid-tight fluid flow paths, each with considerably increased length, within the tube.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention which is directed to a helical heat exchanger assembly comprising a tube having first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter. The helical heat exchanger assembly includes a thermally conductive tube insert having first and second ends and a length therebetween and a substantially similar cross-section to the cross-section of the tube, and a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube. The tube insert includes a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends. Each of the helices' first ends is offset from the other by a predetermined angle and each of the second ends is offset from the other by a predetermined angle. The tube insert is sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices.

The fluid ports may be arranged for counterflow operation, whereby the first and second fluids flow in opposite directions. At least one of the inlet or outlet fluid ports in a set of fluid ports may positioned in an opening in a wall of the tube, or alternatively, at least one of the inlet or outlet fluid ports in a set of fluid ports may be positioned on an end of the tube. The first ends of the helices may be offset from each other by an angle of 180 degrees, and each of the helices may have a predetermined pitch which is less than the tube inner diameter. At least one of the helices may include turbulating dimples or ridges.

Each of the tube and tube insert may have a substantially circular cross-section. The tube insert may be sealed inside the tube such that the tube insert does not extend substantially beyond the tube first or second ends, and the assembly may include a first end cap sealed to the tube and tube insert first ends and a second end cap sealed to the tube and tube insert second ends. The first and second end caps may be flat, circular plates and may be sealed flush with the ends of the tube and tube insert to prevent fluid mixing inside the heat exchanger.

The tube insert may include an inner expansion tube having first and second ends and a length therebetween and a diameter less than the tube insert outer diameter, the helices extending along the length of and winding around the inner expansion tube. The inner expansion tube is capable of receiving an expansion mandrel inserted therein to expand the tube insert into a tight fit with an inner surface of the tube. The tube may include a first end cap sealed to the tube, tube insert and inner expansion tube first ends, respectively, and a second end cap sealed to the tube, tube insert and inner expansion tube second ends, respectively. The first and second end caps may be flat, circular plates and may be sealed flush with the ends of the tube, tube insert and inner expansion tube to prevent fluid mixing inside the heat exchanger.

The tube and tube insert may each be comprised of braze-clad aluminum, and the helices and tube may be brazed together to create fluid-tight first and second fluid flow paths.

The helical heat exchanger assembly may include a plurality of tubes with tube inserts sealed therein, the first fluid inlet ports of each tube arranged in parallel and the second fluid inlet ports of each tube arranged in parallel, and the first fluid outlet ports of each tube arranged in parallel and the second fluid outlet ports of each tube arranged in parallel. The assembly may further include a first inlet manifold connecting each of the first fluid inlet ports, the first inlet manifold including a fluid inlet port for passage of a first fluid into the heat exchanger assembly, a first outlet manifold connecting each of the first fluid outlet ports, the first outlet manifold including a fluid outlet port for passage of a first fluid out of the heat exchanger assembly, a second inlet manifold connecting each of the second fluid inlet ports, the second inlet manifold including a fluid inlet port for passage of a second fluid into the heat exchanger assembly, and a second outlet manifold connecting each of the second fluid outlet ports, the second outlet manifold including a fluid outlet port for passage of a second fluid out of the heat exchanger assembly, wherein the inlet and outlet manifolds are each sealed to prevent fluid mixing inside the heat exchanger assembly.

The first and second inlet and outlet manifold fluid ports may be arranged for counterflow operation whereby the first and second fluids flow in opposite directions.

In another aspect, the present invention is directed to a method of assembling a heat exchanger, comprising the steps of providing a tube having first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter. The method includes providing a thermally conductive tube insert having first and second ends, a length and a substantially similar cross-section to the cross-section of the tube, the tube insert including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle, and inserting the tube insert within the tube and sealing the tube insert therein to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices. The method further includes providing a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube.

The fluid ports may be arranged for counterflow operation, whereby the first and second fluids flow in opposite directions. Each of the first ends of the helices may be offset from the other by an angle of 180 degrees and each of the second ends of the helices may be offset from the other by an angle of 180 degrees, and each of the helices may have a predetermined pitch which is less than the tube inner diameter. At least one of the helices may include turbulating dimples or ridges.

Each of the tube and tube insert may have a substantially circular cross-section and the tube insert may be inserted within the tube by automation. The tube insert may be inserted within the tube such that the tube insert does not extend substantially beyond the tube first or second ends, and the method may further include the steps of sealing a second end cap to the tube and tube insert second ends and sealing a first end cap to the tube and tube insert first ends, respectively. The first and second end caps may be flat, circular plates and may be sealed flush with the ends of the tube and tube insert to prevent fluid mixing inside the heat exchanger.

The tube insert may include an inner expansion tube having first and second ends, a length and a diameter less than the tube insert outer diameter, the helices extending along the length of and winding around the inner expansion tube. The inner expansion tube is capable of receiving an expansion mandrel inserted therein to expand the tube insert into a tight fit with an inner surface of the tube. The method may further include the step of inserting the expansion mandrel into the inner expansion tube and expanding the tube insert until an outer surface of the tube insert is a tight fit against an inner surface of the tube. The method may then include sealing a second end cap to the tube, tube insert, and inner expansion tube second ends and sealing a first end cap to the tube, tube insert, and inner expansion tube first ends, respectively. The first and second end caps may be flat, circular plates and may be sealed flush with the ends of the tube, tube insert and inner expansion tube to prevent fluid mixing inside the heat exchanger.

The tube and tube insert may each be comprised of braze-clad aluminum, and the method may further include the step of brazing the heat exchanger in a cab (controlled atmosphere brazing) furnace to create fluid-tight first and second fluid flow paths.

In yet another aspect, the present invention is directed to a method of operating a heat exchanger assembly, comprising the steps of providing a heat exchanger having a tube with first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter. The heat exchanger includes a thermally conductive tube insert having a length and a substantially similar cross-section to the cross-section of the tube, the tube insert including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle. The tube insert is sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices. The heat exchanger further includes a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube. The method includes connecting inlet and outlet fluid lines for a first fluid to a first set of inlet and outlet ports, connecting inlet and outlet fluid lines for a second fluid to a second set of inlet and outlet ports, and flowing the first and second fluids through the first and second sets of inlet and outlet ports, respectively, to cool one of the fluids.

The first and second sets of inlet and outlet fluid ports may be arranged for counterflow operation, whereby the first and second fluids flow in opposite directions through the first and second fluid paths between the helices.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts a perspective view of one embodiment of the heat exchanger with helical tube insert according to the present invention;

FIG. 2 depicts an exploded perspective view of the heat exchanger with helical tube insert according to the present invention, as shown in FIG. 1;

FIG. 3 depicts a perspective view of one embodiment of the helical tube insert according to the present invention, as shown in FIG. 2;

FIG. 4A depicts a top cross-sectional view of another embodiment of the heat exchanger with helical tube insert;

FIG. 4B depicts an end view of the upper portion of the heat exchanger with helical tube insert of FIG. 4A, showing a first fluid outlet port and a second fluid inlet port;

FIG. 5 depicts a top plan view of a portion of the helical tube insert according to the present invention as shown in FIG. 4A, taken along length L3; and

FIG. 6 depicts a top plan view of another embodiment of the helical tube insert according to the present invention, wherein each of the helices includes turbulating dimples or ridges.

FIG. 7 depicts a perspective view of one embodiment of the heat exchanger assembly including multiple helical heat exchangers arranged in parallel and connected by inlet and outlet manifolds, according to the present invention;

FIG. 8 depicts a cross-sectional view of the embodiment of the heat exchanger assembly shown in FIG. 7, taken along section B-B; and

FIG. 9 depicts a cross-sectional view of the embodiment of the heat exchanger assembly shown in FIG. 7, taken along section A-A.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the embodiment of the present invention, reference will be made herein to FIGS. 1-9 of the drawings in which like numerals refer to like features of the invention.

The present invention is directed to a heat exchanger assembly including a heat exchanger tube and a helical tube insert. The helical tube insert is sealed within a tube of substantially similar cross-section, thereby creating two distinct fluid flow paths within the tube. The pitch of the helical convolutions is less than or equal to the inner diameter of the tube, in order to obtain fluid flow paths of increased length over that of a conventional liquid-to-liquid heat exchanger tube. The ends of the heat exchanger tube are capped and the tube is fitted with inlet and outlet fluid ports for each of the two fluid flow paths. The flow paths within the heat exchanger assembly of the present invention may be parallel flow or co-current (where the fluids move in the same direction), or counterflow (where the direction of the flow of one working fluid is opposite the direction of the flow of the other fluid.) In parallel flow heat exchangers, the outlet temperature of the “hot” fluid can never become lower than the outlet temperature of the “cold” fluid, and the exchanger is performing at its best when the outlet temperatures are equal. Counterflow heat exchangers are inherently more efficient than parallel flow heat exchangers and have several significant advantages over a parallel flow design. The more uniform temperature difference between the two fluids minimizes the thermal stresses throughout the heat exchanger, the outlet temperature of the “hot” fluid can become considerably lower than the outlet temperature of the “cold” fluid and can actually approach the inlet temperature of the “cold” fluid, and the more uniform temperature difference produces a more uniform rate of heat transfer throughout the heat exchanger, over the entire length of the fluid flow path. The fluid connection fittings of the present invention may be arranged for counterflow operation for optimum heat transfer performance.

Certain terminology is used herein for convenience only and is not to be taken as a limitation of the invention. For example, words such as “upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,” and “downward” merely describe the configuration shown in the drawings. For purposes of clarity, the same reference numbers may be used in the drawings to identify similar elements.

Referring now to FIG. 1, a perspective view of one embodiment of the helical heat exchanger assembly of the present invention is shown. The assembly includes a tube 10 of substantially circular cross-section, having a length L1 and first and second ends (not shown), and a helical tube insert (not shown) of substantially similar cross-section sealed therein. Tubes having a circular-shaped axial cross-section (i.e. perpendicular to the axis of the tube) are typically utilized for optimum heat transfer performance of the heat exchanger, although other tube shapes and cross-sections may also be utilized to achieve the objects of the present invention. The ends of the tube 10 may be sealed by a first end cap 14 and second end cap 24 to form a self-contained heat exchanger assembly unit. Preferably, the end caps 14, 24 are flat, circular plates which are sealed flush with the ends of the tube and helical tube insert to prevent fluid mixing at the interior ends of the heat exchanger unit. The first and second end caps 14, 24 may be secured and sealed to the respective ends of the tube by welding, solder baking, brazing or other equivalent process known to those in the art.

Tube 10 includes a plurality of inlet and outlet fluid ports for passage of fluid into and out of the heat exchanger assembly. As shown in FIG. 1, the heat exchanger assembly of the present invention includes a first fluid inlet port 40 and outlet port 42, and a second fluid inlet port 50 and outlet port 52. The first fluid flow path is depicted in direction 41, and the second fluid flow path is depicted in direction 51. As shown in FIG. 2, the fluid connection fittings as described above may be inserted into aligned openings 30 in the wall of the tube 10 and arranged for counterflow operation. The fluid connection fittings are positioned per design requirements, and alternatively may be positioned, for example, on either ends of the tube, as shown in the upper portion of FIG. 4A and in FIG. 4B, so long as the fittings are arranged for counterflow operation.

Referring now to FIG. 2, an exploded perspective view of the heat exchanger assembly of the present invention, including a helical tube insert 100, is shown. Tube insert 100 has first and second ends 101, 102, a length L2 and a substantially similar cross-section to that of tube 10, and is comprised of two helices 120, 130 extending along the length L2 of tube insert 100 and offset from each other by a predetermined distance d. Each of the helices has a first end 121, 131 and a second end 124, 134 (FIG. 6.) As shown in FIGS. 2, 4A and 4B, in a normal configuration, helices first ends 121, 131 are adjacent tube insert first end 101, and helices second ends 124, 134 are adjacent tube insert second end 102. The first ends of each of the helices are offset from each other by a predetermined angle, such as an angle of 180 degrees, as they contact tube end cap 14 and the second ends of each of the helices are offset from each other by a predetermined angle (preferably the same angle as for the first ends) as they contact tube end cap 24 (FIG. 4B.) In the embodiments shown in FIGS. 2 and 4A, the pitch p of the helical convolutions of each of the helices 120, 130 is less than the inner diameter D1 of the heat exchanger tube 10, thereby creating two fluid flow paths, each with substantially increased length over that of a typical heat exchanger tube. Alternatively, the pitch p of each of the helical convolutions may be greater than or equal to the inner diameter D1 of heat exchanger tube 10; however such a configuration will result in a shorter fluid flow path than if the pitch p were less than the inner diameter D1 of the tube 10. The pitch of the helical convolution is defined as the axial advance of a point during one complete rotation.

As further shown in FIG. 2, the helical tube insert 100 may have an outer diameter D2 which is nominally smaller than the inner diameter D1 of tube 10, to allow for a sliding fit therein. During assembly of the heat exchanger, tube insert 100 is slideably inserted into a first tube end 12 in the direction of a second tube end 22. As shown in FIGS. 1-4A, tube insert 100 does not extend substantially beyond the first and second tube ends 12, 22, after insertion into tube 10. Tube insert 100 may be installed manually or by automation during assembly of the heat exchanger unit. After installation, end caps 14, 24 are sealed to tube ends 12, 22, tube insert ends 101, 102, and helices ends 121, 131, 124, 134, respectively, to form fluid-tight fluid flow paths 41, 51 inside the heat exchanger assembly (FIG. 4A.)

As shown in FIG. 2, and more particularly shown in FIG. 3, in an embodiment of the invention, the first ends 121, 131 of the windings of helices 120, 130 are offset from each other by an angle of 180 degrees, and the helices extend along the length of and are wound around an inner expansion tube 110 of relatively small diameter. As further shown in FIG. 3, the second ends 124 and 134 (not shown) of helices 120, 130 are also offset from each other by an angle of 180 degrees. Inner expansion tube 110 has a first end 111 adjacent tube insert first end 101 and a second end 112 adjacent tube insert second end 102 (FIG. 4A.) As shown in FIG. 4A, inner expansion tube 110 has a length substantially equal to the lengths L1, L2 of tube 10 and tube insert 100.

FIG. 4A depicts a top cross-sectional view of another embodiment of the assembled heat exchanger with helical tube insert, showing fluid inlet and outlet ports positioned in the wall of the tube and on one end of the tube, respectively, and arranged for counterflow operation. As shown in FIG. 4A, each of helices 120, 130 has a first side 122, 132 and a second side 123, 133. The respective first 122, 132 and second sides 123, 133 of the helices are offset by a predetermined distance d along the length of tube insert 100, creating two distinct fluid flow paths 41, 51 between the helical convolutions. First fluid flow path 41 begins at tube inlet 40 and ends at tube outlet 42, and is defined between the second sides 123, 133 of the helices, while second fluid flow path 51 begins at tube inlet 50 and ends at tube outlet 52 and is defined between the first sides 122, 132 of the helices. The pitch p of the helical convolutions of each of the helices 120, 130 is less than the inner diameter D1 of the heat exchanger tube 10, thereby creating two fluid flow paths, each with substantially increased length over that of a typical heat exchanger tube. As shown in the bottom portion of FIG. 4A, first fluid inlet port 40 and second fluid outlet port 52 are positioned in openings in the wall of tube 10. Fluid connection fittings positioned other than in openings in the wall of the tube may also be used, for example, fittings and connections at the ends of tube 10, as shown in the upper portion of FIG. 4A, and more particularly shown in FIG. 4B.

FIG. 4B shows an end view of the upper portion of FIG. 4A, showing first fluid outlet port 42 and second fluid inlet port 50 disposed on and integral with end cap 24. Fluid connection fittings 40, 42, 50, 52 are shown arranged for counterflow operation. In operation of the heat exchanger, inlet and outlet fluid lines (not shown) for first fluid flow path 41 are connected to inlet and outlet ports 40 and 42, respectively, and inlet and outlet fluid lines (not shown) for second fluid flow path 51 are connected to inlet and outlet ports 50 and 52, respectively. A first fluid then enters flow path 41 and a second fluid then enters flow path 51 through the respective sets of inlet and outlet ports, and through the respective fluid flow paths respectively, in counterflow operation. The first and second fluids flow in opposite directions through the respective fluid paths between the helices to cool one of the fluids by transferring heat through the helices to the other fluid.

After insertion of tube insert 100 into tube 10, the outer edges of the helices 120, 130 are sealed to the inner surface 11 of tube 10 and the inner edges of the helices 120, 130 are sealed to the outer surface of inner expansion tube 110 to create fluid-tight fluid flow paths 41, 51. Any suitable sealing material may be employed between the helices edges and tubes 10 and 110.

FIG. 5 depicts a top plan view of a portion of the helical tube insert as shown in FIG. 4A, taken along length L3. As shown in FIG. 5, in at least one embodiment of the present invention, inner expansion tube 110 is capable of receiving an expansion mandrel 113 inserted therethrough. After insertion of tube insert 100 into tube 10, expansion mandrel 113 is inserted into inner expansion tube 110 to expand tube insert 100 outwardly in direction 114. Tube insert 100 is expanded such that the tube insert is a tight fit against the inner surface 11 of tube 10, as shown in FIG. 4A, in preparation for sealing tube insert 100 to the inner surface of the tube to complete the assembly.

The tube insert (helices 120, 130 and inner expansion tube 110) and, optionally, the tube, are made of thermally conductive metal, such as aluminum or copper alloys. All parts of the heat exchanger may be made of an aluminum alloy clad with a brazing alloy, and the unit may be flux brazed in a cab (controlled atmosphere brazing) furnace, as per standard aluminum liquid-to-liquid heat exchanger manufacturing techniques. Brazing of the entire unit ensures that the edges of helices 120, 130 of tube insert 100, which are in a tight fit against the inner surface 11 of the tube 10 and the outer surface of inner expansion tube 110, become sealed thereto, and helices ends 121, 131 and 124, 134, are sealed to end caps 14 and 24, respectively, such that two distinct fluid flow paths are created and no common fluid is allowed to flow on both sides of the helices in the same direction, ensuring optimal heat transfer, as shown in FIG. 4A.

In at least one embodiment of the present invention, projections such as turbulating dimples or ridges of various shapes may be incorporated by deformation or embossment of the helices 120, 130 to provide turbulation, as shown in FIG. 6. FIG. 6 shows a tube insert 100′ having turbulating dimples 140 having an oval shape within the fluid flow paths created by and defined between the first 122, 132 and second sides 123, 133 of helices 120, 130. The projections may have alternative shapes such as circular, triangular, or other geometrical shape. The projections or dimples 140 promote transfer of heat from a heated first fluid to a second cooled fluid through the helices during operation of the liquid-to-liquid heat exchanger of the present invention.

It should be understood that the present invention as described above has been described in its basic form of a heat exchanger assembly including one heat exchanger tube with helical tube insert sealed therein. More than one heat exchanger tube with helical tube insert may be combined into a larger heat exchanger assembly (FIGS. 7-9), per design requirements, in accordance with the objects of the present invention.

In such a configuration, a plurality of helical heat exchanger tubes are positioned such that the first fluid inlet ports of each helical heat exchanger are arranged in parallel, the second fluid inlet ports of each helical heat exchanger are arranged in parallel, the first fluid outlet ports of each helical heat exchanger are arranged in parallel and the second fluid outlet ports of each helical heat exchanger are arranged in parallel. The assembly includes inlet and outlet manifolds connecting each of the first fluid inlet and outlet ports, respectively, and each of the second fluid inlet and outlet ports, respectively. Each manifold includes a fluid port for passage of a first or second fluid, respectively, into or out of the heat exchanger assembly. The inlet and outlet manifolds are each sealed to prevent fluid mixing inside the heat exchanger assembly, and the first and second inlet and outlet manifold fluid ports may be arranged for counterflow operation whereby the first and second fluids flow in opposite directions.

FIGS. 7-9 depict an embodiment of the present invention wherein a heat exchanger assembly comprises multiple helical heat exchangers arranged in parallel and combined into a larger assembly. As shown in FIG. 7, heat exchanger assembly 1000 includes a first inlet manifold 200 having a first fluid inlet port 210 for passage of a first fluid 41 into the assembly and a first outlet manifold 300 having a first fluid outlet port 310 (not shown) for passage of the first fluid 41 out of the assembly. The assembly further includes a second inlet manifold 400 having a second fluid inlet port 410 for passage of a second fluid 51 into the assembly and a second outlet manifold 500 having a second fluid outlet port 510 for passage of the second fluid 51 out of the assembly. The inlet and outlet manifolds are each sealed to prevent mixing of the first and second fluids 41, 51 inside the heat exchanger assembly.

FIG. 8 depicts a cross-sectional view of heat exchanger assembly 1000, taken along section B-B of FIG. 7. As shown in FIG. 8, heat exchanger assembly 1000 includes three heat exchanger tubes 10, each with a helical tube insert 100 secured therein. The tubes 10 are positioned such that the second fluid outlet ports 52 of each heat exchanger tube are arranged in parallel. The second fluid outlet ports 52 are connected by a second outlet manifold 500. Second outlet manifold 500 is sealed to prevent fluid mixing inside the assembly and includes a second fluid outlet port 510 for passage of the second fluid 51 out of the assembly. On the opposing side of the assembly, the first fluid outlet ports 42 (not shown) are also arranged in parallel and connected by a first outlet manifold 300. First outlet manifold 300 is sealed to prevent fluid mixing inside the assembly and includes a first fluid outlet port 310 for passage of the first fluid 41 out of the assembly. Any suitable sealing material may be employed to seal the respective manifolds. The number of heat exchanger tubes arranged in parallel in one assembly is shown as three, for illustrative purposes only, as an assembly including two, or more than three, heat exchanger tubes still falls under the scope of the invention.

FIG. 9 depicts a cross-sectional view of heat exchanger assembly 1000, taken along section A-A of FIG. 7. As shown in FIG. 9, each of the first fluid inlet ports 40 are arranged in parallel and connected by first inlet manifold 200, and each of the second fluid inlet ports 50 are arranged in parallel and connected by second inlet manifold 400. First inlet manifold 200 has a fluid inlet port 210 for passage of a first fluid 41 into the assembly, and second inlet manifold 400 has a second inlet port 410 for passage of a second fluid 51 into the assembly. As shown in FIG. 9, first and second inlet and outlet manifold fluid ports 210, 310, 410, 510 are arranged for counterflow operation.

Thus the present invention achieves one or more of the following advantages. The present invention provides an improved heat exchanger assembly which includes a tube with helical tube insert sealed therein, thereby creating two fluid-tight fluid flow paths of considerably increased length within the tube. The heat exchanger provides a considerable increase in fluid flow path length, and consequently an increase in heat transfer, for a given tube length, and thus provides superior heat transfer performance over that of a typical liquid-to-liquid heat exchanger. The heat exchanger allows for counterflow operation, providing optimum heat transfer performance, and makes use of standard aluminum liquid-to-liquid heat exchanger manufacturing techniques, such as inner tube expansion and cab (controlled atmosphere brazing) furnace flux brazing.

While the present invention has been particularly described, in conjunction with a specific embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention. 

Thus, having described the invention, what is claimed is:
 1. A helical heat exchanger assembly, comprising: a tube having first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter; a thermally conductive tube insert having a length and a substantially similar cross-section to the cross-section of the tube, the tube insert having first and second ends and including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle, the tube insert sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices; and a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube.
 2. The heat exchanger assembly of claim 1 wherein the fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions.
 3. The heat exchanger assembly of claim 2 wherein at least one of the inlet or outlet fluid ports in a set of fluid ports is positioned in an opening in a wall of the tube.
 4. The heat exchanger assembly of claim 2 wherein at least one of the inlet or outlet fluid ports in a set of fluid ports is positioned on an end of the tube.
 5. The heat exchanger assembly of claim 1 wherein each of the tube and tube insert has a substantially circular cross-section.
 6. The heat exchanger assembly of claim 1 wherein the first ends of the helices are offset from each other by an angle of 180 degrees.
 7. The heat exchanger assembly of claim 1 wherein each of the helices has a predetermined pitch which is less than the tube inner diameter.
 8. The heat exchanger assembly of claim 1 wherein the tube insert does not extend substantially beyond the tube first or second ends.
 9. The heat exchanger assembly of claim 1 wherein the assembly includes a first end cap sealed to the tube and tube insert first ends and a second end cap sealed to the tube and tube insert second ends.
 10. The heat exchanger assembly of claim 9 wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube and tube insert to prevent fluid mixing inside the heat exchanger.
 11. The heat exchanger assembly of claim 1 wherein the tube insert includes an inner expansion tube having first and second ends, a length and a diameter less than the tube insert outer diameter, the inner expansion tube capable of receiving an expansion mandrel inserted therein to expand the tube insert into a tight fit with an inner surface of the tube, the helices extending along the length of and winding around the inner expansion tube.
 12. The heat exchanger assembly of claim 11 wherein the assembly includes a first end cap sealed to the tube, tube insert, and inner expansion tube first ends and a second end cap sealed to the tube, tube insert, and inner expansion tube second ends.
 13. The heat exchanger assembly of claim 12 wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube, tube insert, and inner expansion tube to prevent fluid mixing inside the heat exchanger.
 14. The heat exchanger assembly of claim 1 wherein at least one of the helices includes turbulating dimples or ridges.
 15. The heat exchanger assembly of claim 1 wherein the tube and tube insert are comprised of braze-clad aluminum.
 16. The heat exchanger assembly of claim 15 wherein the helices and tube are brazed together to create fluid-tight first and second fluid flow paths.
 17. The heat exchanger assembly of claim 1 wherein the assembly includes a plurality of tubes with tube inserts sealed therein, the first fluid inlet ports of each tube arranged in parallel and the second fluid inlet ports of each tube arranged in parallel, and the first fluid outlet ports of each tube arranged in parallel and the second fluid outlet ports of each tube arranged in parallel, and further including: a first inlet manifold connecting each of the first fluid inlet ports, the first inlet manifold including a fluid inlet port for passage of a first fluid into the heat exchanger assembly; a first outlet manifold connecting each of the first fluid outlet ports, the first outlet manifold including a fluid outlet port for passage of a first fluid out of the heat exchanger assembly; a second inlet manifold connecting each of the second fluid inlet ports, the second inlet manifold including a fluid inlet port for passage of a second fluid into the heat exchanger assembly; and a second outlet manifold connecting each of the second fluid outlet ports, the second outlet manifold including a fluid outlet port for passage of a second fluid out of the heat exchanger assembly, wherein the inlet and outlet manifolds are each sealed to prevent fluid mixing inside the heat exchanger assembly.
 18. The heat exchanger assembly of claim 17 wherein the first and second inlet and outlet manifold fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions.
 19. A method of assembling a heat exchanger, comprising the steps of: providing a tube having first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter; providing a thermally conductive tube insert having first and second ends, a length and a substantially similar cross-section to the cross-section of the tube, the tube insert including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle; inserting the tube insert within the tube and sealing the tube insert therein to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices; and providing a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube.
 20. The method of claim 19 wherein the fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions.
 21. The method of claim 19 wherein the tube insert is inserted within the tube by automation.
 22. The method of claim 19 wherein each of the tube and tube insert has a substantially circular cross-section.
 23. The method of claim 19 wherein the first ends of the helices are offset from each other by an angle of 180 degrees.
 24. The method of claim 19 wherein each of the helices has a predetermined pitch which is less than the tube inner diameter.
 25. The method of claim 19 wherein the tube insert does not extend substantially beyond the tube first or second ends.
 26. The method of claim 19 wherein at least one of the helices includes turbulating dimples or ridges.
 27. The method of claim 19 further including the steps of: sealing a second end cap to the tube and tube insert second ends; and sealing a first end cap to the tube and tube insert first ends.
 28. The method of claim 27 wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube and tube insert to prevent fluid mixing inside the heat exchanger.
 29. The method of claim 19 wherein the tube insert includes an inner expansion tube having first and second ends, a length and a diameter less than the tube insert outer diameter, the inner expansion tube capable of receiving an expansion mandrel inserted therein to expand the tube insert into a tight fit with an inner surface of the tube, the helices extending along the length of and winding around the inner expansion tube, and further including the step of: inserting the expansion mandrel into the inner expansion tube and expanding the tube insert until the tube insert is a tight fit against an inner surface of the tube.
 30. The method of claim 29 further including the steps of: sealing a second end cap to the tube, tube insert, and inner expansion tube second ends; and sealing a first end cap to the tube, tube insert, and inner expansion tube first ends.
 31. The method of claim 30 wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube, tube insert, and inner expansion tube to prevent fluid mixing inside the heat exchanger.
 32. The method of claim 19 wherein the tube and tube insert are comprised of braze-clad aluminum, and further including the step of: brazing the heat exchanger in a furnace to create fluid-tight first and second fluid flow paths.
 33. A method of operating a heat exchanger assembly, comprising: providing a heat exchanger having a tube with first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter; a thermally conductive tube insert having a length and a substantially similar cross-section to the cross-section of the tube, the tube insert including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle, the tube insert sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices; and a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube; connecting inlet and outlet fluid lines for a first fluid to a first set of inlet and outlet ports; connecting inlet and outlet fluid lines for a second fluid to a second set of inlet and outlet ports; and flowing the first and second fluids through the first and second sets of inlet and outlet ports, respectively, to cool one of the fluids.
 34. The method of claim 33 wherein the first and second sets of inlet and outlet fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions through the first and second fluid paths between the helices. 